As reported previously, both complement and ADCC effector cells release markers resealed inside red cell ghosts with a very strong size dependence, such that markers below a defined cut-off size are released while all those which are larger are not. This sieving effect was also observed when the entry of protein markers into complement treated ghosts was measured, with the same protein molecular weight cut-off as was observed for marker efflux. The possibility of inhibiting the passage of molecules through the pore by blocking with anti-complement component antibodies was then tested. Anti-C3, -C5, -C8, and -C9 were tested. Anti-C5 blocked marker entry greater than 90% at dilutions to 1/1000. None of the other antisera blocked at 1/10. Anti C5 did not block passage of markers through pores created by detergent. This approach is currently being extended to ADCC pores.